The present invention relates to a technique for measuring a flying height of a recording head in a magnetic disk device, and more particularly to a technique for measuring a flying height of a recording head to execute recording operations in the stable state.
In a magnetic disk device, a magnetic head floats over a magnetic disk as a recording medium to record data at or reproduce data stored at a specified position of the magnetic disk. The magnetic head is embedded in a slider, and the magnetic head and the slider form a head/slider. The head/slider is attached to a suspension assembly and is positioned by an actuator on a specified position in the radial direction of the magnetic disk.
Recent magnetic heads have the structure in which an MR head or a GMR head constituting a reproduction element and an induction type of head constituting a recording head are separated from each other and are embedded in the same slider. The head/slider receives a buoyancy by an air flow generated on a surface of the turning magnetic disk with an air bearing surface (described as ABS hereinafter) which is a surface facing against the magnetic disk and floats over the magnetic disk. A physical clearance between the head/slider and a magnetic disk surface or a recording layer surface is generally called flying height.
Recently, in order to improve the recording density in a magnetic disk, attempts have been made to reduce a flight height of a head/slider, and monitoring and control over a flying height have become more and more important. A flying height depends on a form of an ABS of a head/slider, a mechanical structure of a suspension assembly supporting the head/slider, flatness of a surface of a turning magnetic disk and other factors, so that the flying height cannot be constant. When the flying height is too low, however, the ABS may collide with dust and the like on the magnetic disk, and a floating posture of the head/slider loses the stability, or collision between the magnetic disk and magnetic head may occur. When the flying height is too high, a magnetic coupling force between the magnetic head and the recording layer becomes weaker, and the recording or reproduction capability is degraded.
A flying height fluctuates even after shipment of a magnetic disk device due to such factors as distortion of the suspension mechanism across ages and also to environmental conditions for use thereof such as a temperature or an atmospheric pressure. It is difficult to measure a flying height in a shipped magnetic disk device with a specific device, but the technique for measuring fluctuations of a flying height by processing a signal reproduced from a magnetic disk with a reproduction head is described in patent document 1 (Japanese Patent Laid-Open No. 2001-195211). Patent document 2 (Japanese Patent Laid-Open No. 2004-281012) discloses a technique for controlling a recording current to cope with fluctuations of a flying height due to thermal expansion generated in a recording head by a recording current. Patent document 3 (Japanese Patent Laid-Open No. Hei 5-20635) discloses a technique for controlling a projection rate of a tip section of a magnetic polar due to thermal expansion by energizing a resistance body embedded around a thin film magnetic head element for heating it.